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17.30 Summary

Britain has endured the hottest July day on record with temperatures soaring to 36.7C (98F) - as roads melted and trains were cancelled.

Urgent health warnings were issued and paramedics dealt with a surge in calls amid fears the hot weather could result in deaths.

The Met Office said temperatures hit the record high in Heathrow this afternoon - breaking the previous record of 36.5C (98F) set on July 19 2006 in Wisley, Surrey.

And Wimbledon recorded the hottest day in its history as players sweltered in the searing heat of Centre Court.

The London Ambulance Service said it had seen call-outs to people fainting increase by more than a third (35%) compared to the same day last week, and a 28% hike in the number of calls it has received over the same period.

Britain's trains were blighted by delays and cancellations as Network Rail imposed speed restrictions on some lines amid fears the metal tracks could buckle under the searing heat.

Motoring group AA said it had been called out to reports of road surfaces melting in the heat, bringing disruption to drivers.

And fresh warnings about the dangers of outdoor swimming in the sunshine were issued after a man's body was recovered from a reservoir in Tattingstone, Suffolk, at about 8pm yesterday.

The Met Office recorded a temperature of 36.7C (98F) in Heathrow, making Britain hotter than Barcelona, Ibiza and Athens.

Meanwhile, there was further misery for motorists battling the heat as a stretch of the M1 in Derbyshire is closed after an HGV lorry carrying explosives caught fire at around 1pm.

Pictures showed the lorry engulfed in flames as emergency vehicles rushed to the scene.

16:19 Air pollution in East Anglia

Air pollution is high in parts of East Anglia and moderate across most of Britain, prompting health warnings from the Department for Environment, Food and Rural affairs (Defra).

On their website Defra said: "People with lung disease, children, the elderly and people who are active outdoors may be particularly sensitive to ozone and may begin to notice respiratory symptoms, such as coughing and throat irritation."

16:15 Car trouble

National breakdown firm Green Flag has forecast over 12,500 breakdown call-outs over the next four days, of which one every 70 seconds will be due to the soaring summer heat.

It has already seen an eight per cent increase in breakdowns across the country, and 14 per cent increase in calls since the heat wave hit this week.

Neil Wilson, Head of Rescue and Motor Claims Response at Green Flag, commented: "Since the heatwave hit the UK we've experienced a noticeable increase in breakdown incidents and call-outs.

"Although the sunshine is very welcome, common problems from the heat can include engines overheating and increased risk of tyre punctures. As a result of this, we'll be increasing our efforts to ensure our customers get to where they need to be, no matter what.

"We'd urge all members of the public to make sure they travel with water during car journeys to ensure they stay hydrated should they experience any problems on the road."

16:06 Hot, hot, hot

The Met Office recorded a temperature of 98F (36.7C) in Heathrow, making Britain hotter than Barcelona, Ibiza and Athens.

16:05 Emergencies

The London Ambulance Service said it had seen call-outs to people fainting increase by more than a third compared to the same day last week.

15.52 Fog on the Tyne

Up north though, it's chucking it down:

One second it's 27 degrees and sunny and the next it's thunder and lightening and torrential rain...perfectly sums up Newcastle's climate

15.00

Some nice weather pictures coming in now from around the country. Here are some of the best:

Starlings cool down in a bird bath in Dorset

Jess Ginson, 21, enjoys the early morning sun at Damar Bay in Cornwall

14.52 New ball boy please

As the action hots up at Wimbledon, a ball boy collapses in the heat on Court 17 during John Isner's second-round clash with Matthew Ebden. It is not clear yet why, but it would be no surprise if was due to the temperature.

Weather forecasters have said that the mercury may rise to 35C (96F), beating the previous record of 34.6C (94.28) in the scorching summer of 1976.

14.33 Britain's hot spot

We have the hottest place in the UK so far according to the Met Office. They say Wittering. We presume they mean Wittering in Cambridgeshire. Meanwhile, in New Delhi the temperature's a chilly 31C.

Laura Young, from the Met Office, said: "I doubt we are going to beat that but certainly we will get near that."

But as some parts of the country basked in the hot conditions, forecasters warned of possible severe weather in the south of Scotland.

The Met Office has issued a warning for potential disruption caused by isolated thunderstorms and downpours, which could include gusts of 50mph and large hail of around 1cm in diameter.

14.00 I'm melting

The AA's warning earlier about roads melting appears to be happening in some areas.

A spokesman for the AA said: "The AA are receiving anecdotal reports from patrols that show that in places the road surface is softening, but there are no widespread problems at the moment. But if this continues we could start to see that.

"There was a man who put the stand down on his motorbike and it sank into the tarmac. The roads are soft in places.

12.27 French fries

"The heatwave in France, where temperatures in some parts are due to reach over 40C, knocked out power for around 800,000 homes after an electricity transformer overheated.

"The first black-out took place on Tuesday evening and knocked out lights in the Brittany towns of St Malo, Dinan and Dinard before a second outage kicked in further south near Vannes. Homes turned dark, restaurants emptied and cinema-goers had to leave in mid-film.

"Most of the outages had been fixed by midday on Wednesday.

"In Paris, where the mercury is due to rise to 39 degrees later today, authorities have opened special air-conditioned rooms to the public and were checking on the elderly. France is particularly sensitive about the issue since thousands of people died in a heatwave in 2003."

11.55 Water hot day

It's raining in south London. Well, sort of. A jet of water from a burst pipe thought to have been caused by the hot weather shoots up from the ground in the Furzedown area on the border between Wandsworth borough and Merton:

11.50 Retailer blown away by fan sales

It seems shoppers across the country have been stocking up on heatwave essentials.

According to John Lewis, sales of fans rocketed by 1,300 per cent on Sunday compared to the same time last year, while BBQs also saw a 67 per cent boost across the week. Sunglasses also benefitted from the improved weather, with demand rising by 39 per cent on Sunday alone.

11.39

11.38 Hot tip for the bookies

Bookmakers Coral have slashed the odds on it being Britain's hottest ever summer from 4-1 to 3-1.

They said chances a hosepipe ban will be introduced somewhere in the UK is an odds-on favourite at 1-3.

And Coral said it is odds-on at 10-11 that Wimbledon will be the hottest tournament in its history, beating the previous record of 35.6C (96F) in 1976.

09.12 Misery for commuters

A Network Rail spokeswoman said: "There will be speed restrictions in places, definitely. We are maintaining track temperatures and if necessary putting in speed restrictions so we can protect vulnerable places and keep the trains moving.

"There will be delays, but they might not be significant delays."

Employers have also been urged to allow staff to travel outside rush hour to avoid overcrowded public transport during the exceptionally hot spell, now entering its third day.

09.08 Wimbledon update

In SW19 we have Victoria Ward. Here's the latest from her:

"It is so hot here at Wimbledon that officials have closed the roof on Centre Court to protect the surface from the heat.

"It will reopen at 11.30am, when the grounds open to the public, two hours before Novak Djokovic takes to the court for the second round."

A spokesman said: "We have reduced today's initial capacity slightly to 38,000 to allow people more room in the grounds and therefore more space in the shade and easier access to the free water points.

"The daily capacity is dependant on the number of courts in operation and the prevailing weather conditions so it would not be the first time we have regularly adjusted the daily capacity."

09.00 The forecast

Right, it's boiling outside but how long is this going to last?

The Met Office says the sweltering heat is likely to continue until thunderstorms hit on Friday night - mainly thanks to the jetstream carrying very warm air from the Iberian Peninsula northwards towards Britain.

Sarah Paterson, deputy chief meteorologist at the Met Office, said: "Over the past couple of days we have seen some very hot weather across parts of Iberia with temperatures reaching 43C (109.4F) across southern Spain.

"In the coming 24 hours we are going to see those sorts of temperatures spread further northwards towards southern France, and eventually quite hot temperatures will also reach parts of the UK.

"A good way of visualising what's going on with our weather is by looking at the jetstream.

There was a guy on the tube this morning WEARING A WOOLY HAT. WHAT IS WRONG WITH YOU PEOPLE #hottestdayoftheyear

"The jetstream is moving south towards the Atlantic, towards the Azores and back up again past the north west of the UK.

"This brings southern winds which brings the hot air from Spain gradually northwards to the UK.

"With the warm air we are likely to see the temperatures reaching into the low 30s across parts of southern England.

"In fact we may even see temperatures reaching 34C or even 35C, mainly around the south eastern parts of England and potentially into the midlands as well.

"There is a very small chance we may nudge towards 36C, but the record for July in the southern half of England is 36.5C and it is unlikely we are going to reach that.

"On Thursday we are going to see some slightly less hot conditions with temperatures reaching the high 20s across parts of the south.

"By Friday temperatures must start to increase again reaching the highs of 30C across southern parts again.

"But later in the evening on Friday it does look as if we are going to see a band of showery, heavy and potentially thundery rain heading northwards across the country mainly on Friday evening and overnight and into Saturday.

"Now many people will be happy to hear about this hot weather but it can have a negative impact on some people's health.

"The Met Office has been advising medical professionals on how long the heat is likely to last."

08.50 Twitter reaction

Both #heatwave and #hottestdayoftheyear are now trending on Twitter and the funnies are coming thick and fast, mostly from commuters. Here's a selection that have amused us at Telegraph Towers:

08.29 Purple hot

I can't remember the last time I saw purple on a British weather map, but here it is:

08.27 Stay safe in the water

In yet another warning about they day ahead the fire service has highlighted the dangers of swimming in rivers, reservoirs and lakes to cool off, after the body of a man was recovered in Suffolk.

The body, believed to be a man in his 20s, was discovered at Alton Water reservoir in Tattingstone, Suffolk, about about 8pm on Tuesday after a warm day.

Suffolk Fire and Rescue Service said: "You or your family may be tempted to cool off with a swim in a local river, reservoir, lake or in the sea. The best way to stay safe in or near the water is to take some sensible precautions and prevent accidents from happening."

08.22 Wednesday: the predictions

The temperatures will approach the record for July, compounding travel problems which have already beset holidaymakers and those travelling to work.

Wednesday is expected to be the hottest day in a decade, following a 36.5C peak in Wisley, Surrey, in 2006. It could also prove the hottest day in Wimbledon history, beating the 34.6C record set in 1976.

The heatwave has already triggered a level two alert but it could reach level three as temperatures rise to 35C (95F).

08.10 Public health warning

Public Health England (PHE) has urged people to look out for those who may feel unwell in the hot weather.

Dr Angie Bone, head of extreme events at PHE, said the heat could be dangerous for older people, young children and those with serious illnesses, and urged employers to be flexible.

She said: ''During very hot weather, pregnant women and people who have chronic illnesses, including cardiovascular, respiratory, renal conditions, diabetes or Parkinson's disease, may experience discomfort if indoor temperatures are particularly hot and in using public transport.

''Employers should ensure indoor areas are kept cool and consider allowing these individuals to travel to or from their place of work during cooler, or less busy times of the day. For those working or exercising outdoors, strenuous physical exertion during the hottest part of the day should be kept to a minimum.''

07.37 What to wear on a day like this?

07.35 Get ready

Good morning, and welcome to the hottest day of the year. Yesterday the temperature peaked at a scorching 30.4C (86.7F) at Kew Gardens in west London. But forecasts warned it's going to be even hotter today with the Met Office predicting a blistering 96.8F (36C).